Diurnal Urban Heat Island Research Articles

Effects of the Western Pacific Subtropical High on the urban heat island characteristics in the middle and lower reaches of the Yangtze River, China

The middle and lower reaches of the Yangtze River are frequently affected by the Western Pacific Subtropical High (WPSH) in summer. This leads to phenomena including air subsidence, high temperatures, low rainfall, and weak winds, all of which affect the urban heat island (UHI) effect. Currently, there are few studies on the influence of WPSH on the UHI effect. In this study, we analysed the temporal and spatial distributions of the influence of WPSH on the UHI effect by establishing two scenarios: with and without WPSH. We calculated the UHI intensity and the urban heat island proportion index (UHPI) to analyse the temporal and spatial distributions of the UHI effect. The geographical detector method was then used to analyse the factors influencing UHI. The results indicate the strong heat island effect during the day in provincial capitals and some developed cities. The area of high UHI intensity was larger under the influence of WPSH than in the years without WPSH. WPSH affected UHPI at both day and night, although the effect was more pronounced at night. The factors affecting daytime UHI intensity are mainly POP and NTL, O3 plays a large role in the years with WPSH control. The main factors affecting the UHI intensity at night are AOD, POP and NTL were mainly factors in the years without WPSH control, POP and WPSH were mainly factors in the years with WPSH control. The interactions of the factors are mainly POP and multi-factors during the daytime, and DEM and multi-factors during the nighttime. It was found that the UHI intensity was enhanced under the control of the WPSH, and the influencing factors of the diurnal UHI differed with and without the WPSH control, which ultimately provides realistic suggestions for mitigating the intensity of the UHI in areas affected by the WPSH.

Modeling the impact of land use/land cover (LULC) factors on diurnal and nocturnal Urban Heat Island (UHI) intensities using spatial regression models

This paper models the impact of different land use/land cover (LULC) factors on diurnal and nocturnal Urban Heat Island (UHI) intensities using spatial regression models. This research first developed an extensive dataset of 17 LULC factors as the independent variables and the diurnal and nocturnal UHI intensities as the dependent variables. Second, ordinary least-squared (OLS) regression was implemented to check for spatial autocorrelation. The results showed that spatial autocorrelation exists for diurnal and nocturnal UHI intensities and thus spatial regression models are needed. Hence, the following spatial regression models were implemented: the spatial error model (SEM) and the spatial lag model (SLM). The findings showed that the SEM is the best in modeling the diurnal UHI intensity while the SLM is the best in modeling the nocturnal UHI intensity. The results also showed that the diurnal UHI differs from the nocturnal UHI by its intensity, geographical distribution, and the contributing LULC factors or causes. The outcomes of this research can be used to inform different UHI-related decisions such as identifying and modeling the impacts of the most significant LULC factors on the diurnal and nocturnal UHI intensities as well as determining the most suitable geographical locations for implementing UHI mitigation initiatives.

Assessment of Urban Heat Islands in Brazil based on MODIS remote sensing data

Estimates indicate that by 2050, 70% of the world's population will live in urban areas, expanding the total built-up space and density of those areas. The urban heat island (UHI) phenomenon causes increased temperatures in urban areas compared to outlying regions. It is considered one of the main anthropogenic climate modifications and is directly linked to land-use patterns. The objective of this study was to analyze the presence of the UHI effect, diurnal and nocturnal, in the dry season in 21 Brazilian metropolitan areas from 2000 to 2016. Surface temperature, mean albedo, and normalized difference vegetation index (NDVI) values generated by the MODIS sensor (Moderate-resolution Imaging Spectroradiometer) were used. The results obtained showed substantial differences between diurnal and nocturnal UHI effects. Manaus, Porto Alegre, Belém, and Recife presented the highest values of diurnal UHI, whereas Curitiba, Brasília, São Paulo, and Rio de Janeiro showed higher heat island effects at night. The results are an alert to policymakers of the need to rethink land occupation regulations and also give support to actions to mitigate the phenomenon.

Impact of climate change on urban heat island effect and extreme temperatures: a case‐study

This study investigated the impacts of climate change on the urban heat island (UHI) and the number of very hot (maximum temperature >35°C) and very cold days (minimum temperature <5°C) in the central business district (CBD) of Melbourne city in Australia. A station located in Laverton (less urbanised area), which is 17 km southwest of Melbourne CBD, was selected as the reference station for the computation of UHI intensity in Melbourne CBD. Using daily minimum/maximum temperatures at the two stations, nocturnal/diurnal UHI intensities in Melbourne CBD were computed for the period 1952–2010. It was found that in Melbourne CBD, nocturnal UHI intensities show a clear rising trend over the period 1952–2010 unlike the diurnal UHI intensities. For the analysis of nocturnal UHI intensities in Melbourne CBD, under changing climate, for each calendar month statistical models based on the gene expression programming (GEP) technique were developed for downscaling general‐circulation model (GCM) outputs to monthly average minimum temperature at Melbourne CBD and Laverton. Using the outputs of HadCM3, GFDL2.0 and ECHAM5 pertaining to the A2 greenhouse gas emission scenario on the downscaling models, projections of monthly average minimum temperature were produced for the two stations over the period 2000–2099. In each season, at both stations, the ensemble average of monthly minimum temperature gradually increased over the period 2000–2099. The ensemble‐average UHI intensity in Melbourne CBD projected into the future was higher for all seasons in comparison to that of period 1952–1971. Downscaling models based on the GEP technique were developed for each calendar month for projecting the number of very hot days in November–March and very cold days in May–September in Melbourne CBD. It was found that, in the future, summer weather will spread to early autumn, and winter weather will move to early spring, in Melbourne CBD.

A study of the hourly variability of the urban heat island effect in the Greater Athens Area during summer

Measurements of air temperature and humidity in the urban canopy layer during July 2009 in 26 sites in Athens, Greece, allowed for the mapping of the hourly spatiotemporal evolution of the urban heat island (UHI) effect. City districts neighboring to the mountains to the east were the hottest during the afternoon, while being among the coolest during the early morning hours. While during the early morning some coastal sites were the hottest, the warm air plume slowly moved to the densely urbanized center of the city until 14:00–15:00, moving then further west, to the Elefsis industrial area in the afternoon. Results from the UrbClim model agree fairly well with the observations. Satellite-derived land surface temperature (LST) data from AATSR, ASTER, AVHRR and MODIS, for pixels corresponding to ground stations measuring Tair, showed that LST can be up to 5K lower than the respective Tair during nighttime, while it can be up to 15K higher during the rest of the day. Generally, LST during late afternoon as acquired from AATSR is very near to Tair for all stations and all days, i.e., the AATSR LST afternoon retrieval can be used as a very good approximation of Tair. The hourly evolution of the spatial Tair distribution was almost the same during days with NE Etesian flow as in days with sea breeze circulation, indicating that the mean wind flow was not the main factor controlling the diurnal UHI evolution, although it influenced the temperatures attained. No unambiguous observation of the urban moisture excess (UME) phenomenon could be made.

Quantifying urban heat island intensity in Hong Kong SAR, China

This paper addresses the methodological concerns in quantifying urban heat island (UHI) intensity in Hong Kong SAR, China. Although the urban heat island in Hong Kong has been widely investigated, there is no consensus on the most appropriate fixed point meteorological sites to be used to calculate heat island intensity. This study utilized the Local Climate Zones landscape classification system to classify 17 weather stations from the Hong Kong Observatory’s extensive fixed point meteorological observation network. According to the classification results, the meteorological site located at the Hong Kong Observatory Headquarters is the representative urban weather station in Hong Kong, whereas sites located at Tsak Yue Wu and Ta Kwu Ling are appropriate rural or nonurbanized counterparts. These choices were validated and supported quantitatively through comparison of long-term annual and diurnal UHI intensities with rural stations used in previous studies. Results indicate that the rural stations used in previous studies are not representative, and thus, the past UHI intensities calculated for Hong Kong may have been underestimated.

Time-Space Character Analysis of Urban Heat Island Effect in Nanjing City Using Remote Sensing

Urban heat island effect is the typical representation of urbanization impacts on urban climate.The urban heat island has different time and spatial characteristics for a different urban because of different urbanization level,essence,size and nature condition.The paper analyzes the time and space characteristics of Nanjing city combing high space-resolution Landsat TM with high time-resolution MODIS.This paper analyzes daily characteristics of UCL heat island by eight granule MODIS,seasonal characteristics by sixteen granule MODIS and probes the scale effect of UCL heat island.The diurnal urban heat island intensity is stronger than overnight's.The strongest intensity of urban heat island happens on autumn,the second on summer,the third on spring,the last on winter.The most extensive in scope occurs in summer,the second in autumn,the third in spring, the last in winter.There are three continuous and extensive heat islands in Naning city.The largest area heat island takes on clustere shape,distributing both the riversides of Qinhuai River.The second is the lineal shape along Rehe Road,Jiangnin Road,Longpan Road,Hongshan Road and Heyan Road.The third presents zonal shape and distributes the industry land use in Dachang district and Pukou district.The intensity and scope of urban heat island results are different with different remote scale.The intensity and scope of urban heat island in Naning city respectively using TM and MODIS on April 17,2000 and the scope and intensity using TM are all lager than that using MODIS.

Formulation of a tropical town energy budget (t-TEB) scheme

This work describes the tropical town energy budget (t-TEB) scheme addressed to simulate the diurnal occurrence of the urban heat island (UHI) as observed in the Metropolitan Area of Rio de Janeiro (MARJ; −22° S; −44° W) in Brazil. Reasoning about the tropical urban climate have guided the scheme implementation, starting from the original equations from Masson (Bound-Lay Meteorol 94:357–397, 2000). The modifications include (a) local scaling approaches for obtaining flux–gradient relationships in the roughness sub-layer, (b) the Monin-Obukhov similarity framework in the inertial sub-layer, (c) increasing aerodynamic conductance toward more unstable conditions, and (d) a modified urban subsurface drainage system to transfer the intercepted rainwater by roofs to the roads. Simulations along 2007 for the MARJ are obtained and compared with the climatology. The t-TEB simulation is consistent with the observations, suggesting that the timing and dynamics of the UHI in tropical cities could vary significantly from the familiar patterns observed in mid-latitude cities—with the peak heat island intensity occurring in the morning than at night. The simulations are suggesting that the thermal phase shift of this tropical diurnal UHI is a response of the surface energy budget to the large amount of solar radiation, intense evapotranspiration, and thermal response of the vegetated surfaces over a very humid soil layer.

The urban heat island of Bucharest during the extreme high temperatures of July 2007

This paper explores the characteristics of the air (Tair) and land surface temperature (LST) from the city of Bucharest (Romania) during the extreme high temperatures that affected the region in July 2007. The behavior of Bucharest’s Urban Heat Island (UHI) is quantitatively described following similar methodological approaches to previous studies. The analysis integrates thermal data supplied by the Moderate Resolution Imaging Spectroradiometer (MODIS) sensors aboard the NASA satellites and meteorological data provided by the ground-based weather stations. Based on the Tair, one may claim that during extreme high summer temperatures, the UHI preserves its spatial and temporal pattern regarding the differences between the central urban perimeter and the suburban area. The investigation of the LST from July 2007 reveals that the nocturnal changes refer mainly to the magnitude and the limits of the UHI, while the shape is not changed. However, the extreme temperatures induce significant modifications of the features of the diurnal UHI, obliterating and dissipating it in certain spots, enlarging it and creating shifted heat islands in some other spots. The main explanation is the outstanding duration and intensity of the hot mass of air impacting the area. The correlations between the Tair measured at the weather stations in Bucharest and the corresponding LST retrieved significant values both under “normal” conditions and extreme temperature persistence, and offer good premises for robust validation studies. The MODIS products performed like an extremely useful instrument for analyzing the UHI.